This invention relates generally to devices for the treatment of bone fractures in which soft tissue damage is present, and, more particularly, to a pre-assembled, unilateral external fixation device for controlled closed reduction of a bone fracture which is operable to apply controlled distraction and compression at the fracture site of the bone.
A variety of activities such as high speed travel and the widespread use of heavy machinery in industry have in recent years increased the frequency of severely compounded and infected long bone fractures, such as the femur, tibia, radius and ulna, with accompanying damage to the surrounding soft tissue. In order to properly manage the wound and prevent infection of the soft tissue, it is necessary to avoid covering the affected area except with appropriate dressings or skin grafts. Casts may not be used for the treatment of long bone fractures where soft tissue damage is present.
One early method of treatment of these cases, which is still used today, involves placing the patient in traction to completely immobilize the affected limb. As is well known, there are many problems attendant to long term confinement of a patient to a bed including necrotic pressure sores and muscle atrophy.
Another approach in the prior art for the treatment of such fractures involved the use of internal fixation devices such as bone plates which were secured directly to the bone. The problem with this method is that the fracture segments must be exposed to insert and affix the device, which increases the chance of infection of both the bone and surrounding soft tissue.
In order to limit the use of traction in the treatment of fractured bones with attendant soft tissue damage, and to avoid the use of bone plates and other internal fixation devices, research begun in the 1800's resulted in the development of external skeletal fixation devices. These devices generally comprise one or more retaining pins secured to the distal bone segment and proximal bone segment on opposite sides of the fracture, which are adjustably connected to a frame located externally of the affected limb.
One external fixation device commonly used today is the so-called Hoffmann system originally developed in the late 1930's. The Hoffmann fixation system includes two sets of self-drilling and self-tapping retaining pins, known as transfixing pins, each having a centrally located continuous thread. One set of two or three transfixing pins enters the soft tissue at one side of the fracture site, passes completely through the distal or proximal segment of the bone and then extends outwardly through the soft tissue on the opposite side. The same procedure is repeated for the other set of transfixing pins on the opposite side of the fracture. Each transfixing pin is connected at opposite ends to a frame which is adapted to permit translation and pivoting of the pins for properly aligning the distal and proximal segments. The frame is adjustable during the surgical procedure, and controlled distraction or compression may be applied post-operatively to maintain the bone segments in engagement and in alignment.
Different frame configurations have been employed for supporting the transfixing pins such as bilateral, triangular, circular and quadrilateral frames. See the discussion, for example, in Mears, Dana C. (1983) External Skeletal Fixation, The Williams & Wilkins, Baltimore, Chapter 1, pp. 1-41; Chao, E.Y.S., AN, K.N. (1982) Biomechanical Analysis Of External Fixation Devices For the Treatment Of Open Bone Fractures, Finite Elements in Biomechanics, John Wiley & Sons, Ltd. The above-described Hoffmann device, for example, employs a quadrilateral frame.
One problem with prior art external fixation devices employing bilateral, triangular, circular or quadrilateral frames involves the use of transfixing pins. As mentioned above, transfixing pins are first inserted into the soft tissue on the distal and proximal side of the fracture from one side of the injured limb. The surgeon can manipulate each transfixing pin around nerves and arteries in the soft tissue on one side of the limb until the transfixing pin contacts the bone and begins to enter the cortical bone. At that point, however, the path of the pin is fixed and no further manipulation is possible. There is a substantial risk of nerve and arterial damage as the pin passes through the bone and then into the soft tissue in a fixed path on the opposite side of the leg.
A second major problem with prior art external fixation devices, such as the Hoffmann device, is that the frame elements for supporting the transfixing pins are not preassembled but must be assembled during the surgery. An assortment of clamping elements and adjustment mechanisms forming the Hoffmann frame are provided in separate pieces and must be fitted together and then clamped to the transfixing pins during the surgical procedure. Unless a surgeon has great familiarity with a particular unassembled frame device, there may be a reluctance to employ an external fixation device at all.
One purpose of external fixation devices is to enable patients to move about and reduce the incidence of necrosis and other problems caused by confinement to bed. Many of the frame designs for securing transfixing pins, including the Hoffmann quadrilateral system and circular frames such as shown in U.S. Pat. Nos. 4,365,624 and 4,308,863, are extremely bulky and make it difficult for the patient to walk or otherwise move about. In addition, bulky metal frames often cover the fracture site and obstruct x-rays. While the transfixing pins must be firmly secured to apply the necessary force to the bone segments, it is desirable to make the frame as light as possible without obstructing the fracture site.
Another disadvantage of prior art external fixation devices is the difficulty in adjusting the position and force exerted by the retaining pins, both during and after surgery. During a surgical procedure and post-operatively, external fixation devices must be capable of adjusting the transfixing pins to vary the position of the bone segments and to control distraction and compression at the fracture site. It is often desirable to make relatively minor corrections of the position or force exerted by a set of retaining pins on one side of the fracture. However, in the Hoffmann quadrilateral fixation device and others, movement of the frame elements to adjust the position of one set of transfixing pins in any direction requires adjustment of other frame elements associated with the other set of transfixing pins. This unduly complicates post-operative adjustment procedures which further reduces the willingness of physicians to employ such devices.
Some of the problems with external fixation devices employing transfixing pins have been eliminated by unilateral fixation devices which consist of a single frame element located on one side of the injured limb having pin clamps to secure half pins mounted in the distal and proximal bone fragments. Half pins extend into only one side of the extremity and thus avoid the problem of damage to the soft tissue on the opposite side which can be caused by transfixing pins. Additionally, unilateral fixation devices are generally lighter in weight and present less of an obstruction to the affected area than other external fixation devices. Examples of unilateral external fixation devices include the "Shearer" external fixation system commercially available from Chas. F. Thackray Limited, Leeds, England and the "AO-ASIF" tubular external fixator commercially available from Synthes, Paoli, Pa.
One problem with unilateral fixation devices of the type described above is that they do not, provide the desired stability to prevent movement of the bone segments relative to one another, particularly axial rotation and transverse subluxation of the bone segments. In addition, fine or relatively slight adjustment of the position of the bone segments at the fracture is difficult with prior art unilateral fixation devices.
In a typical surgical procedure for an injury of the type described above, gross adjustment of the bone segment positions is made manually, usually by manipulating the distal bone segment. But it is desirable to make fine adjustments in the position of the segments once the fixation device is in place. Preferably, such fine adjustment is obtained by manipulating the frame or the pin clamps of the fixation device which are connected to the half pins inserted within either the proximal or distal bone segment. Unfortunately, any adjustment of the position of the bone segments obtained by moving either the frame or the pin clamps carried by the frame in prior art unilateral devices results in substantial movement of the bone segments at the fracture site. This prevents fine or precise adjustment of the position of the bone segments and can lead to incorrect anatomical alignment thereof.